Alan Fryar | University of Kentucky (original) (raw)

Papers by Alan Fryar

Environmental & Engineering Geoscience

Because of well-integrated surface and subsurface drainage in karst terrains, springs can exhibit... more Because of well-integrated surface and subsurface drainage in karst terrains, springs can exhibit relatively rapid hydraulic, chemical, and thermal responses to storms. In urbanized karst basins, impervious cover, stream channelization, and utility infrastructure can alter infiltration, provide alternate pathways for subsurface flow, and affect ambient water quality. We combined continuous logging of electrical conductivity (EC) and water temperature with analyses of stable isotopes (deuterium and oxygen-18) to differentiate focused and diffuse recharge in a karst basin in Lexington, Kentucky, during 2018. Logging occurred at the McConnell Springs Blue Hole and a sinkhole that drains to it; isotopes, specific conductance, and temperature were manually monitored at those sites and along two losing stream reaches. Water temperature at McConnell Springs and stable isotope abundances showed seasonal variability. The Blue Hole responded within hours to stormwater infiltration at the sink...

Sustainability

Karst springs are important water sources for both human needs and environmental flows. The respo... more Karst springs are important water sources for both human needs and environmental flows. The responses of karst springs to hydrometeorological factors vary depending on local conditions. In this study, we investigated Martandnag spring in the Liddar catchment in the Kashmir valley of northern India. We used statistical time series (autocorrelation and cross-correlation) and machine-learning (ML) techniques (random forest regression (RFR) and support vector regression (SVR)) to characterize how rainfall, temperature, and snow cover affect the karst spring flow and predict the future responses of the spring stage based on climate scenarios, in the Intergovernmental Panel on Climate Change Assessment Report 6. The statistical time series showed that the memory effect of Martandnag spring varies from 43 to 61 days, indicating moderate karstification and a relatively high storage capacity of the karst aquifer in the Liddar catchment. The delay between recharge and discharge varies from 13...

Geological Society of America Abstracts with Programs

AGU Fall Meeting Abstracts, Dec 1, 2013

GSA Bulletin, 2022

The Ganges River delta complex contains a transboundary aquifer system shared between India and B... more The Ganges River delta complex contains a transboundary aquifer system shared between India and Bangladesh. Although it serves as the main freshwater source for the population inhabiting the delta, the aquifer system is severely contaminated with arsenic (As). This study aimed to determine the control of the delta hydrostratigraphy on the regional-scale depth distribution of As within the aquifer system. We developed the first high-resolution, regional-scale, transboundary hydrostratigraphic model of the Ganges River delta and analyzed the patterns of As distribution as a function of the hydrostratigraphy. Model results indicate that, despite the presence of a single aquifer system across the delta, the hydrostratigraphy is spatially variable and can be architecturally divided into three distinct aquifer subsystems from northwest to southeast: a single, thick continuous aquifer (type I); a vertically segregated, semi-confined aquifer subsystem (type II); and a multilayered, nearly c...

Sustainable Water Resources Management, 2021

Artificial neural networks (ANN), adaptive neuro-fuzzy inference system (ANFIS) with subtractive ... more Artificial neural networks (ANN), adaptive neuro-fuzzy inference system (ANFIS) with subtractive clustering (ANFIS-SC) and support vector machine models were used to determine total dissolved solids (TDS) of the Zayandehrood River in Iran. In total, nine hydrochemical parameters [Ca 2+ , SO 4 2− , Na + , Cl − , EC, pH, HCO 3 − , Mg 2+ and sodium adsorption ratio (SAR)] were utilized to estimate the TDS of the river at a monthly time scale. Statistical data were categorized into low-flow and wet periods based on river discharge. Principal component analysis (PCA) was used to determine the input of the models. The results indicate that the PCA method, in both wet and low-flow periods, performed suitably based on the evaluation criteria for all models. The parameters of the first component included Ca 2+ , SO 4 2− , Cl − , EC, Mg 2+ and SAR in both periods. In contrast, the parameters pH and HCO 3 − of the second component provided unacceptable precision. The ANFIS-SC model was more precise than the other two models, with an RMSE value of 12.33 meq/l for the first component in the low-flow period. However, the ANN model was most precise in the wet period, with a calculated RMSE value of 13.87 meq/l.

How do springs respond to precipitation? • Infiltration displaces water in pores, fractures, cond... more How do springs respond to precipitation? • Infiltration displaces water in pores, fractures, conduits-discharge (Q) peak results from pressure-pulse propagation

Encyclopedia of Geology, 2021

POSTER: The Jackson Purchase region of western Kentucky consists of Coastal Plain sediments near ... more POSTER: The Jackson Purchase region of western Kentucky consists of Coastal Plain sediments near the northern margin of the Mississippi Embayment. Within this region is the Paducah Gaseous Diffusion Plant (PGDP), a uranium enrichment facility operated by the US Department of Energy. At PGDP, a Superfund site, soil and groundwater studies have provided subsurface lithologic data from hundreds of monitoring wells and borings. Despite preliminary efforts by various contractors, these data have not been utilized to develop detailed stratigraphic correlations of sedimentary units across the study area. In addition, sedimentary exposures along streams in the vicinityof PGDP have not been systematically described beyond the relatively simple geologic quadrangle maps published by the US Geological Survey in 1966-67. This study integrates lithologic logs, other previous site investigation data, and outcrop mapping to provide a compilation of near-surface lithologic and stratigraphic data for...

Imperiled: The Encyclopedia of Conservation, 2021

Springs are ecosystems influenced by the exposure of groundwater at the Earth’s surface. Springs ... more Springs are ecosystems influenced by the exposure of groundwater at the Earth’s surface. Springs are abundant and have played important, highly interactive ecological, cultural, and socio-economic roles in arid, mesic, and subaqueous environments throughout human evolution and history. However, springs also are widely regarded as being highly threatened by human impacts. Cantonati et al. (2020a) recommended increased global awareness of springs, including basic mapping, inventory and assessment of the distribution and ecological integrity of springs. We conducted a preliminary global analysis on the ecological integrity of springs by reviewing information on the distribution, ecohydrogeology, associated species, kinds and intensity of human uses, and level of ecological impairment of spring ecosystems. We reviewed information on an estimated 250,000 spring ecosystems among 78 countries across much of the world. Available literature on spring ecological integrity is sparse, widely scattered, and spatially erratic, with major gaps in knowledge. We report large differences in the quality and extent of information among countries and continents, with only moderate data availability even among developed countries, and limited information across most of the developing world. Among countries with available data, ecological impairment of springs is everywhere rampant, sometimes exceeding 90% in developed regions. Impairment among Holarctic nations is generally negatively related to distance from human development, elevation, and latitude, but such patterns are less evident in Africa, Australia, and South America. Declining trends in ecosystem condition, compounding threat factors, and spring-dependent population declines, extirpation, and extinctions of plants, invertebrates, fish, and herpetofauna are widely reported. Overall, available information indicates a global crisis in spring ecosystem integrity, with levels of ecosystem impairment ranging from Vulnerable to fully Collapsed. The threats to aquifers and the ecological integrity of springs vary spatially. Many springs are impaired by local impacts due to flow diversion, geomorphic alteration, land use practices, recreation impacts, and the introduction of non-native species. These threats can be reduced through education, rehabilitation of geomorphology and habitat quality, and species reintroductions if the supporting aquifer remains relatively intact. However, springs also are widely threatened by regional to global factors, including groundwater extraction and pollution, as well as climate change. Such coarse-scale, pre-emergence impacts negatively affect the sustainability of spring ecosystems and the aquifers that support them. Improving understanding and stewardship of springs will require much additional systematic inventory and assessment, improved information management, and reconsideration of basic conservation concepts (e.g., habitat connectivity), as well as cultural and socio-economic valuation. Substantial societal recognition, discussion, and policy reform are needed within and among nations to better protect and sustainably rehabilitate springs, their supporting aquifers, and the spring-dependent human and biotic populations that depend upon them

Groundwater for Sustainable Development, 2019

The effect of climate change on future groundwater conditions in the Toyserkan basin in western I... more The effect of climate change on future groundwater conditions in the Toyserkan basin in western Iran has been studied. In recent years, overexploitation for agricultural activities has led to water-table decline. Groundwater recharge rate predictions in the study area were obtained from the RCP4.5 Scenario of the 5th Assessment Report of the Intergovernmental Panel on Climate Change and HadGEM2 General Circulation Model. Outputs were downscaled with the RegCM4 Regional Climate Model coupled to the Community Land Model version 4.5 (CLM 4.5). RegCM4 model validation and prediction were attempted for 7 years (1999-2005) and 11 years (2015-2025), respectively. Validation results showed that RegCM4 reasonably simulated daily precipitation and monthly temperature and runoff. Firstly, geological, geophysical and hydrogeological data were used and evaluated to develop the conceptual model. Secondly, a 3D numerical model of groundwater flow was developed in order to describe the groundwater regime and predict the effects of water management strategies. Two scenarios were defined for the prediction period. The first scenario assumes that current exploitation rates will be continued, while the second one assumes a 20 percent decrease in pumping due to increased irrigation efficiency. The results showed a water-table rise from 2015 to 2025, which is heightened by increase in irrigation efficiency.

Journal of Nepal Geological Society, 2016

Groundwater flow in karst terrains is difficult to map because it can be concentrated through con... more Groundwater flow in karst terrains is difficult to map because it can be concentrated through conduits that do not necessarily coincide with the surface features. We applied electrical resistivity (ER) and self-potential (SP) techniques at three sites to locate an inferred trunk conduit feeding a major spring in the Inner Bluegrass region of Kentucky (USA). Royal Spring is the primary water supply for the city of Georgetown; the upper part of its basin coincides with the Cane Run watershed. ER profiles (972 m total length) were measured using a dipole–dipole electrode configuration with 2- to 3-m spacing. SP measurements were taken along those ER lines and an additional test profile (230 m) using one stationary reference electrode and another roving electrode at a fixed interval. The SP technique has been used by many researchers to detect the electro kinetic potential generated by groundwater flow. The low resistivity of water in the conduit, as compared to the high background resi...

Water Research, 2019

Reducing pathogenic risks in surface waters impacted by leaking or overflowing sewage requires th... more Reducing pathogenic risks in surface waters impacted by leaking or overflowing sewage requires the ability to detect human excreta in raw sewage, discriminate human excreta from other types of animal excreta, and differentiate between treated wastewater and raw sewage. We used the relative concentrations of a degradable, human-specific pharmaceutical and a persistent artificial sweetener to indicate the presence of human excreta, its degree of environmental degradation, and the amount of dilution by freshwater sources. Samples were collected and analyzed for acetaminophen and sucralose between 2016 and 2018 from wastewater treatment plants (WWTPs) and streams in metropolitan Lexington, Kentucky (USA). Both co-analytes were consistently present in raw sewage, with acetaminophen in higher concentrations than sucralose. The presence of acetaminophen was related primarily to untreated human excreta, with concentrations rapidly decreasing upon treatment to nearly undetectable levels in WWTP effluents and streams. Sucralose in surface waters was related to inputs of both raw sewage and WWTP effluents. The ratio of acetaminophen to sucralose concentrations in raw sewage and spiked river waters exhibited linear decay kinetics with respect to time, with larger decay constants observed at higher temperatures. This co-analyte indicator approach was evaluated at a local site previously suspected of receiving raw sewage. The presence and ratios of the co-analytes indicated the presence of domestic sewage that was not fully treated.

Journal of Environment Quality, 2015

Journal of Environmental Quality SHORT COMMUNICATIONS Core Ideas • The HuBac biomarker is linearl... more Journal of Environmental Quality SHORT COMMUNICATIONS Core Ideas • The HuBac biomarker is linearly correlated to the more specific qHF183 biomarker. • Determine location, rather than identify an unknown source, with a more sensitive biomarker. • HuBac and qHF183 may be used in urban watershed studies. • A more sensitive marker is preferred when "less than" values are problematic in modeling.

Journal of Sedimentary Research, 1994

be further reduced by having two (or more!) operators count the same pebble populations. The meth... more be further reduced by having two (or more!) operators count the same pebble populations. The method can be applied only where at least partly three-dimensional exposures of pebbles are present. Unconsolidated gravels can therefore be studied well with the method, and also conglomerates with a strong competence contrast between matrix and pebbles (e.g., diamictites). Where the lithologic composition of the gravel/conglomerate is an aim, a lower size limit for pebbles is defined by the determinability of lithologies. An upper size limit will have to be laid down to eliminate possible extreme values (note that pebble volumes increase approximately as the cube of the x-axis). Statistical tests for extreme values can be found in David et al. (1954) and Gruhbs (1973). However, these tests require a Gaussian distribution of pebble-size data, a prerequisite that will frequently not be met by pebble populations. Here, arbitrary upper size limits will have to be chosen.

Environmental & Engineering Geoscience

Because of well-integrated surface and subsurface drainage in karst terrains, springs can exhibit... more Because of well-integrated surface and subsurface drainage in karst terrains, springs can exhibit relatively rapid hydraulic, chemical, and thermal responses to storms. In urbanized karst basins, impervious cover, stream channelization, and utility infrastructure can alter infiltration, provide alternate pathways for subsurface flow, and affect ambient water quality. We combined continuous logging of electrical conductivity (EC) and water temperature with analyses of stable isotopes (deuterium and oxygen-18) to differentiate focused and diffuse recharge in a karst basin in Lexington, Kentucky, during 2018. Logging occurred at the McConnell Springs Blue Hole and a sinkhole that drains to it; isotopes, specific conductance, and temperature were manually monitored at those sites and along two losing stream reaches. Water temperature at McConnell Springs and stable isotope abundances showed seasonal variability. The Blue Hole responded within hours to stormwater infiltration at the sink...

Sustainability

Karst springs are important water sources for both human needs and environmental flows. The respo... more Karst springs are important water sources for both human needs and environmental flows. The responses of karst springs to hydrometeorological factors vary depending on local conditions. In this study, we investigated Martandnag spring in the Liddar catchment in the Kashmir valley of northern India. We used statistical time series (autocorrelation and cross-correlation) and machine-learning (ML) techniques (random forest regression (RFR) and support vector regression (SVR)) to characterize how rainfall, temperature, and snow cover affect the karst spring flow and predict the future responses of the spring stage based on climate scenarios, in the Intergovernmental Panel on Climate Change Assessment Report 6. The statistical time series showed that the memory effect of Martandnag spring varies from 43 to 61 days, indicating moderate karstification and a relatively high storage capacity of the karst aquifer in the Liddar catchment. The delay between recharge and discharge varies from 13...

Geological Society of America Abstracts with Programs

AGU Fall Meeting Abstracts, Dec 1, 2013

GSA Bulletin, 2022

The Ganges River delta complex contains a transboundary aquifer system shared between India and B... more The Ganges River delta complex contains a transboundary aquifer system shared between India and Bangladesh. Although it serves as the main freshwater source for the population inhabiting the delta, the aquifer system is severely contaminated with arsenic (As). This study aimed to determine the control of the delta hydrostratigraphy on the regional-scale depth distribution of As within the aquifer system. We developed the first high-resolution, regional-scale, transboundary hydrostratigraphic model of the Ganges River delta and analyzed the patterns of As distribution as a function of the hydrostratigraphy. Model results indicate that, despite the presence of a single aquifer system across the delta, the hydrostratigraphy is spatially variable and can be architecturally divided into three distinct aquifer subsystems from northwest to southeast: a single, thick continuous aquifer (type I); a vertically segregated, semi-confined aquifer subsystem (type II); and a multilayered, nearly c...

Sustainable Water Resources Management, 2021

Artificial neural networks (ANN), adaptive neuro-fuzzy inference system (ANFIS) with subtractive ... more Artificial neural networks (ANN), adaptive neuro-fuzzy inference system (ANFIS) with subtractive clustering (ANFIS-SC) and support vector machine models were used to determine total dissolved solids (TDS) of the Zayandehrood River in Iran. In total, nine hydrochemical parameters [Ca 2+ , SO 4 2− , Na + , Cl − , EC, pH, HCO 3 − , Mg 2+ and sodium adsorption ratio (SAR)] were utilized to estimate the TDS of the river at a monthly time scale. Statistical data were categorized into low-flow and wet periods based on river discharge. Principal component analysis (PCA) was used to determine the input of the models. The results indicate that the PCA method, in both wet and low-flow periods, performed suitably based on the evaluation criteria for all models. The parameters of the first component included Ca 2+ , SO 4 2− , Cl − , EC, Mg 2+ and SAR in both periods. In contrast, the parameters pH and HCO 3 − of the second component provided unacceptable precision. The ANFIS-SC model was more precise than the other two models, with an RMSE value of 12.33 meq/l for the first component in the low-flow period. However, the ANN model was most precise in the wet period, with a calculated RMSE value of 13.87 meq/l.

How do springs respond to precipitation? • Infiltration displaces water in pores, fractures, cond... more How do springs respond to precipitation? • Infiltration displaces water in pores, fractures, conduits-discharge (Q) peak results from pressure-pulse propagation

Encyclopedia of Geology, 2021

POSTER: The Jackson Purchase region of western Kentucky consists of Coastal Plain sediments near ... more POSTER: The Jackson Purchase region of western Kentucky consists of Coastal Plain sediments near the northern margin of the Mississippi Embayment. Within this region is the Paducah Gaseous Diffusion Plant (PGDP), a uranium enrichment facility operated by the US Department of Energy. At PGDP, a Superfund site, soil and groundwater studies have provided subsurface lithologic data from hundreds of monitoring wells and borings. Despite preliminary efforts by various contractors, these data have not been utilized to develop detailed stratigraphic correlations of sedimentary units across the study area. In addition, sedimentary exposures along streams in the vicinityof PGDP have not been systematically described beyond the relatively simple geologic quadrangle maps published by the US Geological Survey in 1966-67. This study integrates lithologic logs, other previous site investigation data, and outcrop mapping to provide a compilation of near-surface lithologic and stratigraphic data for...

Imperiled: The Encyclopedia of Conservation, 2021

Springs are ecosystems influenced by the exposure of groundwater at the Earth’s surface. Springs ... more Springs are ecosystems influenced by the exposure of groundwater at the Earth’s surface. Springs are abundant and have played important, highly interactive ecological, cultural, and socio-economic roles in arid, mesic, and subaqueous environments throughout human evolution and history. However, springs also are widely regarded as being highly threatened by human impacts. Cantonati et al. (2020a) recommended increased global awareness of springs, including basic mapping, inventory and assessment of the distribution and ecological integrity of springs. We conducted a preliminary global analysis on the ecological integrity of springs by reviewing information on the distribution, ecohydrogeology, associated species, kinds and intensity of human uses, and level of ecological impairment of spring ecosystems. We reviewed information on an estimated 250,000 spring ecosystems among 78 countries across much of the world. Available literature on spring ecological integrity is sparse, widely scattered, and spatially erratic, with major gaps in knowledge. We report large differences in the quality and extent of information among countries and continents, with only moderate data availability even among developed countries, and limited information across most of the developing world. Among countries with available data, ecological impairment of springs is everywhere rampant, sometimes exceeding 90% in developed regions. Impairment among Holarctic nations is generally negatively related to distance from human development, elevation, and latitude, but such patterns are less evident in Africa, Australia, and South America. Declining trends in ecosystem condition, compounding threat factors, and spring-dependent population declines, extirpation, and extinctions of plants, invertebrates, fish, and herpetofauna are widely reported. Overall, available information indicates a global crisis in spring ecosystem integrity, with levels of ecosystem impairment ranging from Vulnerable to fully Collapsed. The threats to aquifers and the ecological integrity of springs vary spatially. Many springs are impaired by local impacts due to flow diversion, geomorphic alteration, land use practices, recreation impacts, and the introduction of non-native species. These threats can be reduced through education, rehabilitation of geomorphology and habitat quality, and species reintroductions if the supporting aquifer remains relatively intact. However, springs also are widely threatened by regional to global factors, including groundwater extraction and pollution, as well as climate change. Such coarse-scale, pre-emergence impacts negatively affect the sustainability of spring ecosystems and the aquifers that support them. Improving understanding and stewardship of springs will require much additional systematic inventory and assessment, improved information management, and reconsideration of basic conservation concepts (e.g., habitat connectivity), as well as cultural and socio-economic valuation. Substantial societal recognition, discussion, and policy reform are needed within and among nations to better protect and sustainably rehabilitate springs, their supporting aquifers, and the spring-dependent human and biotic populations that depend upon them

Groundwater for Sustainable Development, 2019

The effect of climate change on future groundwater conditions in the Toyserkan basin in western I... more The effect of climate change on future groundwater conditions in the Toyserkan basin in western Iran has been studied. In recent years, overexploitation for agricultural activities has led to water-table decline. Groundwater recharge rate predictions in the study area were obtained from the RCP4.5 Scenario of the 5th Assessment Report of the Intergovernmental Panel on Climate Change and HadGEM2 General Circulation Model. Outputs were downscaled with the RegCM4 Regional Climate Model coupled to the Community Land Model version 4.5 (CLM 4.5). RegCM4 model validation and prediction were attempted for 7 years (1999-2005) and 11 years (2015-2025), respectively. Validation results showed that RegCM4 reasonably simulated daily precipitation and monthly temperature and runoff. Firstly, geological, geophysical and hydrogeological data were used and evaluated to develop the conceptual model. Secondly, a 3D numerical model of groundwater flow was developed in order to describe the groundwater regime and predict the effects of water management strategies. Two scenarios were defined for the prediction period. The first scenario assumes that current exploitation rates will be continued, while the second one assumes a 20 percent decrease in pumping due to increased irrigation efficiency. The results showed a water-table rise from 2015 to 2025, which is heightened by increase in irrigation efficiency.

Journal of Nepal Geological Society, 2016

Groundwater flow in karst terrains is difficult to map because it can be concentrated through con... more Groundwater flow in karst terrains is difficult to map because it can be concentrated through conduits that do not necessarily coincide with the surface features. We applied electrical resistivity (ER) and self-potential (SP) techniques at three sites to locate an inferred trunk conduit feeding a major spring in the Inner Bluegrass region of Kentucky (USA). Royal Spring is the primary water supply for the city of Georgetown; the upper part of its basin coincides with the Cane Run watershed. ER profiles (972 m total length) were measured using a dipole–dipole electrode configuration with 2- to 3-m spacing. SP measurements were taken along those ER lines and an additional test profile (230 m) using one stationary reference electrode and another roving electrode at a fixed interval. The SP technique has been used by many researchers to detect the electro kinetic potential generated by groundwater flow. The low resistivity of water in the conduit, as compared to the high background resi...

Water Research, 2019

Reducing pathogenic risks in surface waters impacted by leaking or overflowing sewage requires th... more Reducing pathogenic risks in surface waters impacted by leaking or overflowing sewage requires the ability to detect human excreta in raw sewage, discriminate human excreta from other types of animal excreta, and differentiate between treated wastewater and raw sewage. We used the relative concentrations of a degradable, human-specific pharmaceutical and a persistent artificial sweetener to indicate the presence of human excreta, its degree of environmental degradation, and the amount of dilution by freshwater sources. Samples were collected and analyzed for acetaminophen and sucralose between 2016 and 2018 from wastewater treatment plants (WWTPs) and streams in metropolitan Lexington, Kentucky (USA). Both co-analytes were consistently present in raw sewage, with acetaminophen in higher concentrations than sucralose. The presence of acetaminophen was related primarily to untreated human excreta, with concentrations rapidly decreasing upon treatment to nearly undetectable levels in WWTP effluents and streams. Sucralose in surface waters was related to inputs of both raw sewage and WWTP effluents. The ratio of acetaminophen to sucralose concentrations in raw sewage and spiked river waters exhibited linear decay kinetics with respect to time, with larger decay constants observed at higher temperatures. This co-analyte indicator approach was evaluated at a local site previously suspected of receiving raw sewage. The presence and ratios of the co-analytes indicated the presence of domestic sewage that was not fully treated.

Journal of Environment Quality, 2015

Journal of Environmental Quality SHORT COMMUNICATIONS Core Ideas • The HuBac biomarker is linearl... more Journal of Environmental Quality SHORT COMMUNICATIONS Core Ideas • The HuBac biomarker is linearly correlated to the more specific qHF183 biomarker. • Determine location, rather than identify an unknown source, with a more sensitive biomarker. • HuBac and qHF183 may be used in urban watershed studies. • A more sensitive marker is preferred when "less than" values are problematic in modeling.

Journal of Sedimentary Research, 1994

be further reduced by having two (or more!) operators count the same pebble populations. The meth... more be further reduced by having two (or more!) operators count the same pebble populations. The method can be applied only where at least partly three-dimensional exposures of pebbles are present. Unconsolidated gravels can therefore be studied well with the method, and also conglomerates with a strong competence contrast between matrix and pebbles (e.g., diamictites). Where the lithologic composition of the gravel/conglomerate is an aim, a lower size limit for pebbles is defined by the determinability of lithologies. An upper size limit will have to be laid down to eliminate possible extreme values (note that pebble volumes increase approximately as the cube of the x-axis). Statistical tests for extreme values can be found in David et al. (1954) and Gruhbs (1973). However, these tests require a Gaussian distribution of pebble-size data, a prerequisite that will frequently not be met by pebble populations. Here, arbitrary upper size limits will have to be chosen.

Karst refers to terrain largely drained by subsurface conduits and caves. Karst landscapes are ch... more Karst refers to terrain largely drained by subsurface conduits and caves. Karst landscapes are characterized by surface features such as springs, sinkholes, shallow depressions, and rolling hills. Karst regions are also known for their subsurface or below-ground features such as conduits and caves. What makes a karst region unique is the way runoff drains from the land. In karst regions, some of the runoff flows into surface features such as sinkholes where it then travels underground. Some of this infiltrated water re-emerges at springs, and some continues moving underground.